A CATALYTIC CRACKING PROCESS

Abstract: Heavy oils are subjected to catalytic cracking in the absence of added hydrogen using a catalyst containing a zeolite having the structure of ZSM-12 and a large-pore crystalline zeolite having a Constraint Index less than about 1. The process is able to effect a bulk conversion of the oil while at the same time yielding a higher octane gasoline and increased light olefin content.

Description: A CATALYTIC CRACKING PROCESS This invention relates to a process for the catalytic cracking of hydrocarbon oils. Catalytic cracking of hydrocarbon oils utilizing crystalline zeolites is a known process, practiced for example, in fluid-bed catalytic cracking (FCC) units, moving bed or thermofor catalytic cracking (TCC) reactors, and fixed-bed crackers. Crystalline zeolites, particularly large pore zeolites having a pore size in excess of 7 Angsto , and especially zeolite Y, have been found to be particularly effective for the catalytic cracking of a gas oil to produce motor fuels, and have been described and claimed in many patents, including U.S. Patents 3,140,249; 3,140,251; 3,140,252; 3,140,253; and 3,271,418. It is also known in the prior art to incorporate the large pore crystalline zeolite into a matrix for catalytic cracking, and such disclosure appears in one or more of the above-identified U.S. patents. It is also known that improved results can be obtained in the catalytic cracking of gas oils if a crystalline zeolite having a pore size of less than 7 Angstrom units is included with the large pore crystalline zeolite with or without a matrix. A disclosure of this type is found in U.S. Patent 3,769,202. Although the incorporation of a crystalline zeolite having a pore size of less than 7 Angstrom units into a catalyst composite comprising a large-pore size crystalline zeolite has been very effective with respect to raising the octane number of the gasoline product, nevertheless it has done so at the expense of the overall yield of gasoline. Improved results in catalytic cracking with respect to both octane number and overall yield were achieved in U.S. Patent 3,758,403, in which the cracking catalyst comprised a large-pore size crystalline zeolite (pore size greater than 7 Angstrom units) in admixture with a ZSM-5 zeolite, wherein the ratio of ZSM-5 zeolite to large-pore size crystalline zeolite was in the range of 1:10 to 3:1. The use of ZSM-5 zeolite in conjunction with a zeolite cracking catalyst of the X or Y faujasite variety is described in U.S. Patents 3,894,931; 3,894,933; and 3,894,934. The former two patents disclose the use of a ZSM-5 zeolite in amounts of about 5-10 wt.%; the latter patent discloses the weight ratio of ZSM-5 zeolite to large-pore size crystalline zeolite within the range of 1:10 to 3:1. The addition of a separate additive or composite catalyst comprising ZSM-5 has been found to be extremely efficient as an octane and total yield improver, when used in very small amounts, in conjunction with a conventional cracking catalyst. Thus, in U.S. Patent 4,309,279, it was found that only 0.1 to 0.5 wt.% of a ZSM-5 catalyst, added to a conventional cracking catalyst under conventional cracking operations, could increase octane by about 1-3 RON + 0 (Research Octane Number Without Lead) . U.S. Patent 4,309,280 also teaches ZSM-5 and other zeolites in conjunction with a conventional cracking catalyst. U.S. Patent 4,740,292 discloses catalytic cracking with a mixture of zeolite Beta and a faujasite zeolite. U.S. Patents 4,309,279; 4,309,280; and 4,521,298 disclose catalytic cracking processes characterized by the addition of very small amounts of additive promoter comprising a class of zeolites having a Constraint Index of about 1 to 12 to cracking catalysts. U.S. Patent 4,416,765 discloses catalytic cracking using a catalyst comprising an amorphous cracking catalyst and a minor amount of a class of crystalline zeolites characterized by a silica to alumina ratio greater than about 12 and a Constraint Index of 1 to 12. In accordance with the present invention, there has now been discovered an improved process for upgrading the total yield and octane number of gasoline boiling range product, while also increasing the yields of C_, C. and C,_ olefins and isobutane. This desirable result is obtained by the use of a catalyst composition comprising ZSM-12 and one or more large-pore crystalline zeolites having a Constraint Index less than about 1. Accordingly, the present invention resides in a catalytic cracking process which comprises contacting a hydrocarbon feed in the absence of added hydrogen with a cracking catalyst comprising a zeolite having the structure of ZSM-12 and a large-pore, crystalline zeolite having a Constraint Index less than 1, the weight ratio of the zeolite having the structure of ZS -12 to the large-pore crystalline zeolite component being in the range 1:10 to 10:1. The process enables heavy feedstocks, such as gas oils boiling above 215°C (420 β F), to be converted to gasoline range products boiling below 215°C (420°F) and distillates in the 215 to 343°C (420 to 650°F range) . Use of the catalyst composition of this invention results in improved cracking activity over the base REY catalyst, increased octane numbers of the product gasoline and increased gasoline plus alkylate yield relative to the base REY catalyst alone. The present hydrocarbon conversion process is an improved catalytic cracking process which involves converting a hydrocarbon feed over a cracking catalyst. The catalyst used in the process comprises a zeolite having the structure of ZSM-12 and a large- pore, crystalline zeolite having a Constraint Index less than 1, such as REY, USY and REUSY. ZSM-12 is described in U.S. Patent No. 3,832,449, which is incorporated herein by reference. The weight ratio of the zeolite having the structure of ZSM-12 to the large-pore, crystalline zeolite having a Constraint Index less than 1 is in the range 1:10 to 10:1, preferably in the range 1:10 to 3:1 and most prefably in the range 1:10 to 10:7. As stated previously, another component of the catalyst mixture of the invention is a large-pore, crystalline zeolite having a Constraint Index less than 1. The method by which Constraint Index is determined is described fully in U.S. Patent No. 4,016,218. Constraint Index (CI) for some typical zeolites including some which are suitable as catalyst components in the catalytic cracking process of this invention are as follows: CI (at test temperature) ZSM-4 0.5 (316°C) ZSM-5 6-8.3 (371°C-316°C) ZSM-11 5-8.7 (371°C-316°C) ZSM-12 2.3 (316°C) ZSM-20 0.5 (371°C) ZSM-22 7.3 (427°C) ZSM-23 9.1 (427°C) ZSM-34 50 (371°C) ZSM-35 4.5 (454°C) ZSM-48 3.5 (538°C) ZSM-50 2.1 (427°C) MCM-22 1.5 (454°C) TMA Offretite 3.7 (316°C) TEA Mordenite 0.4 (316°C) Clinoptilolite 3.4 (510°C) Mordenite 0.5 (316°C) R7!Y 0.4 (316°C) Dealuminized Y 0.5 (510°C) Erionite 38 (316 β C) Zeolite Beta 0.6-2.0 (316°C-399°C) The large-pore, crystalline zeolites having a CI less than about 1 which are useful in the process of this invention are well known in the art and have a pore size sufficiently large to admit the vast majority of components normally found in the feedstock. The zeolites are generally stated to have a pore size in excess of 7 Angstroms and are represented by zeolites having the structure of, e.g., ZSM-4, ZSM-20, Mordenite, Zeolite Beta, Dealuminized Y, REY, USY and REUSY. A crystalline silicate zeolite well known in the art and useful in the present invention is faujasite. The ZSM-20 zeolite resembles faujasite in certain aspects of structure but has a notably higher silica/alumina ratio than faujasite, as does Dealuminized Y. ZSM-4 is described in U.S. Patent 3,642,434. ZSM-20 is described in U.S. Patent 3,972,983. Mordenite is described in U.S. Patent 4,503,023. Dealuminized Y zeolite is described in U.S. Patent 3,442,795. Zeolite Beta is described in U.S. Patent 3,308,069 and RE 28,341. Zeolites of particular use include REY, USY, and REUSY. REY is described in U.S. Patents 3,595,611 and 3,607,043. Low sodium Ultrastable Y molecular sieve (USY) is described in U.S. Patents 3,293,192 and 3,449,070. REUSY is described in U.S. Patent 3,957,623. It may be desirable to incorporate the zeolites into a material resistant to the temperature and other conditions employed in the process. Such matrix materials include synthetic and naturally occurring substances, such as inorganic materials, e.g., clay, silica, and metal oxides. The latter may be either naturally occurring or in the form of gelatinous precipitates or gels, including mixtures of silica and metal oxides. Naturally occurring clays can be composited with the zeolites, including those of the montmorillonite and kaolin families. These clays can be used in the raw state as originally mined or initially subjected to calcination, acid treatment, or chemical modification. The zeolites may be composited with a porous matrix material, such as alumina, silica-alumina, silica-magnesia, silica-zirconia, silica-thoria, silica-beryllia, silica-titania, as well as ternary compositions such as silica-alu ina-thoria, silica- alumina-zirconia, silica-alumina-magnesia, and silica-magnesia-zirconia. The matrix may be in the form of a cogel or sol. The relative proportions of zeolite component and inorganic oxide gel matrix on an anhydrous basis may vary widely with the zeolite content ranging from 5 to 99, more usually 10 to 65, wt.% of the dry composite. The matrix itself may possess catalytic properties, generally of an acidic nature, and may be impregnated with a combustion promoter, such as platinum, to enhance a carbon monoxide combustion. The matrix material may include phosphorus that is derived from a water soluble phosphorus compound including phosphoric acid, ammonium dihydrogen phosphate, diam onium hydrogen phosphate, ammonium phosphate, ammonium hypophosphate, ammonium phosphite, ammonium hypophosphite and ammonium dihydrogen orthophosphite. The zeolite having the structure of ZSM-12 and the large-pore, crystalline zeolite having a Constraint Index less than 1 may be used on separate catalyst particles, i.e., a mixture of the catalysts. The ZSM-12 zeolite and the large-pore, crystalline zeolite may also be used as a composite, i.e., catalyst particles containing both zeolites in the same particle. The ZSM-12 and the large-pore, crystalline zeolite may be combined, blended, dispersed, or otherwise intimately admixed or composited with a porous matrix in such proportions that the resulting product contains 1 to 95 wt%, and preferably 10 to 70 wt.% of the total zeolites in the final composite. In a moving bed process, the use of a composite catalyst may be preferred; but in a fluid process a mixture is satisfactory. The feedstock of the present conversion process comprises a heavy hydrocarbon oil, such as gas oil, coker tower bottoms fraction reduced crude, vacuum tower bottoms, deasphalted vacuum resids, FCC tower bottoms, and cycle oils. Oils derived from coal, shale or tar sands may also be treated in this way. Oils of this kind generally boil about 650°F (343°C) although this process is also useful with oils which have initial boiling points as low as 500°F (260°C) . These heavy oils comprises high molecular weight long-chain paraffins, naphthenes and high molecular weight aromatics with a large proportion of fused ring aromatics. The heavy hydrocarbon oil feedstock will normally contain a substantial amount boiling above 230°C (450°F) and will normally have an initial boiling point of about 550°F (288°C), more usually about 650°F (343°C). Typical boiling ranges will be 650 to 1050°F (343 to 566°C), or 650 to 950 β F (343 to 510°C), but oils with a narrower boiling range may, of course, be processed, for example, those with a boiling range of about 650 to 850 β F (343 to 454 β C). Heavy gas oils are often of this kind, as are cycle oils and other nonresidual materials. It is possible to co-process materials boiling below 500°F (288°C), but the degree of conversion will be lower for such components. Feedstocks containing lighter ends of this kind will normally have an initial boiling point above about 300°F (149°C). The processing is carried out under conditions similar to those used for conventional catalytic cracking. Process temperatures of 750 to 1200"F (400 to 650°C) may conveniently be used, although temperatures above 1050°F (565°C) will normally not be employed. Generally, temperatures of 840 to 1050°F (450 to 565"C) will be employed. The space velocity of the feedstock will normally be from 0.1 to 20 LHSV, preferably 0.1 to 10 LHSV. The conversion may be conducted by contacting the feedstock with a fixed stationary bed of catalyst, a fluidized bed, or with a transport bed. The catalyst may be regenerated by burning in air or other oxygen-containing gas. A preliminary hydrotreating tep to remove the nitrogen and sulfur and to saturate aromatics to naphthenes without substantial boiling range conversion will usually improve catalyst performance and permit lower temperatures, higher space velocities, or combinations of these conditions to be employed. The invention will now be more particularly descibed with reference to the following examples and the accompanying drawings, in which: Figure 1A is a plot illustrating the relationship of C 5 + gasoline yield to activity (% conversion) . Figure IB is a plot illustrating the relationship of octane number of C,_+ gasoline to activity (% conversion) . Figure 2A is a plot illustrating the relationship of total C.'s yield to activity (% conversion) . Figure 2B is a plot illustrating the relationship of dry gas (C_-) yield to activity (% conversion) . Figure 2C is a plot illustrating the relationship of coke yield to activity (% conversion) . Figure 3A is a plot illustrating the relationship of % pentenes/pentanes yield to activity (% conversion) . Figure 3B is a plot illustrating the relationship of % butenes/butanes yield to activity (% conversion) . Figure 3C is a plot illustrating the relationship of % propenes/propanes yield to activity (% conversion) . Figure 4A is a plot illustrating the relationship of C + gasoline + alkylate yield to activity (% conversion) . Figure 4B is a plot illustrating the relationship of octane number of C^.+ gasoline + alkylate to activity (% conversion) . Figure 5A is a plot illustrating the relationship of coke yield to crackability. Figure 5B is a plot illustrating the relationship of catalyst/oil ratio to crackability. EXAMPLES Catalyst A A commercially available FCC catalyst which comprises about 15 wt% REY is used as the base catalyst. This catalyst is withdrawn from a commercial FCC unit after oxidative regeneration. The catalyst contains 560 ppm V, 260 ppm Ni and 1.7 wt% rare earth oxide. The catalyst has a unit cell size of 24.41 Angstroms and is henceforth referred to as Catalyst A. Catalyst B A catalyst for use in the present process is prepared by spray drying an aqueous slurry containing 25 wt.% ZSM-12, synthesized in accordance with U.S. Patent 3,832,449, in a SiO -A1_0 3 gel/clay matrix. The spray dried catalyst is ammonium exchanged and calcined. The calcination is carried out at 1000°F (540 β C) for 2 hours in air followed by steaming the catalyst for 4 hours at 1200°F (650°C) in a 45% steam/55% air mixture at 0 psig (100 kPa) . One part by weight ZSM-12 catalyst is then blended with 3 parts by weight REY catalyst (Catalyst A) to provide a cracking catalyst having 6.25 wt% ZSM-12/11.25 wt% REY and is henceforth referred to as Catalyst B. Catalyst C A catalyst for use in the process of the present invention is prepared by spray drying an aqueous slurry containing 40 wt.% ZSM-12, synthesized in accordance with U.S. Patent 3,832,449, in a SiO_- Al-O -H-PO. sol/clay matrix. The spray dried catalyst is ammonium exchanged and calcined. The calcination is carried out at 1000"F (540°C) for 2 hours in air. One part by weight ZSM-12 catalyst is then blended with 3 parts by weight REY catalyst (Catalyst A) to provide a cracking catalyst having 8.0 wt% ZSM-12/11.25 wt% REY and is henceforth referred to as Catalyst C. Catalyst D This is a catalyst blend used for comparative purposes comprising ZSM-5 and Catalyst A to show that the ZSM-12/large-pore, crystalline zeolite catalysts of the present invention selectively enhance the yield of C. olefins over the ZSM-5/large-pore, crystalline zeolite catalyst. A commercially available ZSM-5 fluid catalyst which comprises about 25 wt.% ZSM-5 in a SiO_-Al 2 0 3 -clay matrix is calcined at 1000 β F (540°C) for 2 hours in air followed by steaming the catalyst for 4 hours at 1200 β F (650°C) in a 45% steam/ 55% air mixture at 0 psig (100 kPa) . One part by weight ZSM-5 catalyst is then blended with 3 parts by weight REY catalyst (Catalyst A) to provide a cracking catalyst having 6.25 wt.% ZSM-5/ 11.25 wt.% REY and is henceforth referred to as Catalyst D. Catalysts A, B, C, and D were evaluated in a fixed-fluidized bed (FFB) unit at a temperature of 960°F (515°C) , a 1.0 minute contact time and atmospheric pressure (100 kPa) using a Sour Heavy Gas Oil (SHGO) having the properties as shown in Table 1. Table 1 Properties of Joliet Sour Heavy Gas Oil Pour Point, °F(°C) 95(35) Conradson Coke Residue, wt.% 0.56 Kinematic Viscosity § 40 β C 104.8 Kinematic Viscosity @ 100°C 7.95 Aniline Point, 0 F(°C) 168.5(76) Bromine Number 6.9 Gravity, API 20.1 Carbon, wt.% 85.1 Hydrogen, wt.% 12.1 Sulfur, wt.% 2.6 Nitrogen, wt.% 0.2 Total, wt.% 100.0 Basic Nitrogen, ppm 465 Nickel, ppm 0.5 Vanadium, ppm 0.3 Iron, ppm 1.2 Copper, ppm < 0.1 Sodium, ppm 0.8 A range of conversions were scanned by varying the catalyst to oil ratio. The fixed-fluidized bed results, after interpolation to 65 vol% conversion, are summarized in Tables 2 and 3 below. Table 2 Catalyst Catalyst Catalyst Catalyst A B C D C < -+ Gasoline, vol.% 52.4 - 49.9 40.0 37.4 Gasoline + alkylate, vol.% 71.2 72.4 74.4 73.8 Alkylate, vol.% 18.8 22.6 34.4 36.5 RON, C 5 + Gasoline 90.5 91.4 93.2 93.6 RON, C 5 + Gasoline + Alkylate 91.4 92.2 93.5 93.6 Coke, wt.% 6.2 5.3 6.0 5.8 Light Fuel Oil wt.% 29.3 29.0 28.3 28.9 Heavy Fuel Oil wt.% 7.8 8.3 9.5 8.8 G+D, wt.% 71.9 69.8 60.9 59.7 Total C 3 , vol.% 7.7 8.9 15.8 18.8 Total C 4 , vol.% 11.7 14.7 19.9 19.4 n-Gς, vol.% 0.4 0.3 0.5 0.3 N-C 4 , vol.% 0.8 0.2 0.2 0.1 C-, vol.% 1.9 2.9 4.5 4.9 i-C 5 , vol.% 5.3 6.1 5.0 5.0 i-C 4 , vol.% 5.5 7.2 10.4 11.1 Outside i-C 4 for Alkylate, vol.% 7.3 8.1 13.2 14.0 Light Gases Light Gas, wt.% 2.5 2.5 2.5 3.2 C 2 , wt.% 0.5 0.4 0.5 0.5 C 2 =, wt.% 0.5 0.3 0.5 0.9 CT, wt.% 0.5 0.4 0.5 0.6 H . wt.% 0.17 0.11 0.13 0.17 EgS, wt.% 0.93 1.26 0.78 0.99 Hydrogen Factor 146 107 94 95 Table 3 Catalyst Catalyst Catalyst Catalysl A B C D Olefin Yield Propylene, vol% 5.8 6.0 11.3 13.9 Butenes, vol.% 5.4 7.5 9.3 8.2 Pentenes, vol.% 4.2 5.3 5.0 3.9 Total, vol.% 15.4 18.8 25.6 26.0 Olefin/Paraffin Selectivity Propylene/Propane 3.1 2.1 2.5 2.8 Butenes/Butanes 0.9 1.0 0.9 0.7 Pentenes/Pentanes 0.7 0.8 0.9 0.7 Olefin Selectivity C-=/Total A ~ + C ά ~ + C < - ~ ) 0.38 0.32 0.44 0.53 t ( ~ + C 0.35 0.40 0.36 0.32 C c = Tota 1 ( c ~ + C ά +C, ) 0.27 0.28 0.20 0.15 Figures 1A and IB compare the C g catalytically cracked gasoline yield and RON as a function of 650"F + ( v 343 β C+ '. conversion. Figures 1A and IB show the use of ZSM-12 produces a significant drop in gasoline yield and a concomitant increase in RON. The ZSM-12/REY catalysts (Catalysts B and C) show enhanced activity as measured by RON as compared to the base REY catalyst alone (Catalyst A) . The RON boosts are in the 1-2 range. Figures 2A, 2B and 2C compare the C. , dry gas and coke yields as a function of 650°F +(343°C+) conversion. Figures 2A and 2B show the use of ZSM- 12/REY catalysts (Catalysts B and C) increase the amount of C. , s (butenes + butanes) produced while increasing dry gas (H S + H_ + C. + C, + C 3 ) only marginally. C 's are more desirable than dry gas. The use of ZSM-12/REY catalysts also result in no change in coke make. Figures 3A, 3B and 3C compare the olefin to paraffin ratio for the light gases (C 3 through C 5 ) as a function of 650°F + (343 . c+) conversion . Figure 3C shows that the ZSM-12/REY catalysts (Catalyst B and C) reduce the olefinicity of the C_ components while increasing the olefinicity of the C and C 5 components, as shown in Figures 3A and 3B. C and C 5 olefins are valuable for methyl tert butyl ether (MTBE) and tertiary amyl methyl ether (TAME) production which are major components in oxygenated gasoline. Figure 3B in conjunction with Table 3 further shows that ZSM-12/REY catalysts (Catalysts B and C) are also more selective toward C. olefins (butenes) than the ZSM-5/REY catalyst (Catalyst D) . Butenes are the preferred feedstock for alkylation and for MTBE production. Figures 4A and 4B compare the C 5 + catalytically cracked gasoline + alkylate, which equals the net gasoline from the process, and RON as a function of 650°F + (343 β C' conversion. Figure 4A shows that the ZSM-12/REY catalysts (Catalysts B and C) make more net gasoline than REY (Catalyst A) alone. Figure 4B shows that the ZSM-12/REY catalysts (Catalysts B and C) also produce a higher octane gasoline product as measured by RON. Figures 5A and 5B compare the coke make and the required catalyst to oil ratio versus crackability. Crackability is a kinetic parameter that reflects the global second order kinetics of the cracking reaction. Higher crackabilities correspond to higher conversions. Figure 5A shows that at the same crackability ( - conversion) , the addition of the ZSM-12 (Catalysts B and C) has little effect on coke make. At equivalent crackabilities higher catalyst to oil ratios correspond to lower catalyst activity. Figure 5B shows that the unsteamed ZSM-12 (Catalyst C) produces a slightly more active catalyst while the steamed ZSM-12 (Catalyst B) is marginally less active than the base REY (Catalyst A) with which it is combined.

Claims: CLAIMS ; 1. A catalytic cracking process which comprises contacting a hydrocarbon feed in the absence of added hydrogen with a cracking catalyst comprising a zeolite having the structure of ZSM-12 and a large-pore, crystalline zeolite having a Constraint Index less than 1, the weight ratio of the zeolite having the structure of ZSM-12 to the large-pore crystalline zeolite component being in the range 1:10 to 10:1. 2. A process according to claim 1 in which the weight ratio of the zeolite having the structure of ZSM-12 to the large-pore, crystalline zeolite is from 1:10 to 3:1. 3. A process according to claim 1 in which the weight ratio of the zeolite having the structure of ZSM-12 to the large-pore, crystalline zeolite is from 1:10 to 7:10. 4. A process according to claim 1 wherein in which the large-pore, crystalline zeolite is selected from REY, USY, REUSY, ZSM-4, ZSM-20, Mordenite, Dealuminized Y and Zeolite Beta. 5. A process according to claim 1 in which the large-pore, crystalline zeolite is selected from REY, USY and REUSY. 6. A process according to claim 1 in which the the cracking catalyst comprises a composite of the zeolite having the structure of ZSM-12 and the large-pore, crystalline zeolite. 7. A process according to claim 1 in which the cracking catalyst comprises the zeolite having the structure of ZSM-12 and the large-pore, crystalline zeolite as separately matrixed components of a mixture. 8. A process according to claim 7 in which the mixture comprises about 25 wt% of the component comprising the zeolite having the structure of ZSM-12 and about 75 wt.% of the component comprising the large-pore, crystalline zeolite. 9. A process according to claim 1 in which the catalytic cracking is carried out as a fluid catalytic cracking process. 10. A process according to claim 1 in which the catalytic cracking process is carried out a a temperature in the range of 750 to 1050 β F (400 to 565°C) .

Inventors: DEGNAN THOMAS FRANCIS JR, HELTON TERRY EUGENE, DEGNAN, THOMAS, FRANCIS, JR., HELTON, TERRY, EUGENE
Applicants: MOBIL OIL CORP, MOBIL OIL CORPORATION
Application year: 1994
Main classification: C10G11
IPC codes: B01J29, C10G11